1. Field of the Invention
The present invention relates to a block-shaped scaffold for a tissue engineering, which comprises a bioabsorbable polymer material, and a production method thereof. The bioabsorbable polymer material has a porous structure used as a substitute for a biotissue, excellent shape stability, and little volume change even when dipping it in water.
2. Description of the Conventional Art
For regenerating a biotissue lost by an operation, an external injury or the like, the medical treatment which has been carried out conventionally, comprises, reconstructing the lost biotissue by somatic cells, stem cells or the like, and transplanting it to a patient. In the medical treatment, a scaffold until seeded cells reconstruct the biotissue (matrix) becomes important for regenerating the biotissue.
For example, in a regeneration field of a skin or the like, the treatment comprising, producing a collagen material having a porous structure, seeding epidermic cornification cells to the collagen material, and thereby producing a cultured artificial skin having a structure of epidermis and dermis, is known. The collagen has excellent biocompatibility, and is decomposed and absorbed after regenerating the tissue, and thus the collagen is an excellent scaffold. However, as for the scaffold produced with the collagen, there are problems that the scaffold cannot keep a necessary shape since only a very soft scaffold is produced. Further, a material originating in the biology has a problem in safety with respect to an unknown pathogen when it is used as a medical supply with respect to a human body. Such an unknown pathogen is represented by BSE (bovine spongiform encephalopathy).
On the other hand, a sponge-shaped scaffold for a tissue engineering having a hole diameter of about 5 to 100 μm is used, where the scaffold is produced by the steps of dissolving a bioabsorbable polymer material (it is also said to as a biodegradable polymer) with an organic solvent such as dioxane, dichloromethane or the like, and freezing and drying this solution, where the bioabsorbable polymer material comprises lactic acid, glycolic acid, caprolactone or the like (refer to Japanese Patent Application Laid Open No. 10-234844 (1998)). Further, a bioabsorbable polymer material having a porous structure is used as the scaffold for cells, where the material has a circular opening large hole being about 50 to 500 μm and a circular opening small hole being 20 μm or less. When producing such the sponge-shaped scaffold for the tissue engineering, the bioabsorbable polymer material is produced by the steps of taking a water-soluble and nontoxic material having a particle-shape (for example, a sodium chloride powder) into a solution, where the particle diameter is about 50 to 500 μm, removing a solvent to thereby produce a biodegradable polymer containing the particle-shaped material, and removing the particle-shaped material using water or the like (for example, refer to Japanese translation of PCT international application No. 2002-541925). However, such the scaffold comprising the biodegradable polymer having the porous structure has problem that, since this scaffold is a sponge-shaped block, it has low elastic coefficient, so that it cannot keep the necessary shape in many cases. In addition, when the hole diameter is decreased in order to increase the elastic coefficient, a function as the scaffold for efficiently regenerating the biotissue is decreased.
As the other method for increasing the elastic coefficient of the biodegradable polymer, the method comprising, pressing and heating the sponge-shaped scaffold for the tissue engineering to thereby increase the density, can be used. However, the scaffold produced by this method has a problem that it is expanded with water content such as a culture medium when dipping it in a cell culture on a body fluid or the like when embedding it in a living body.